inexpensive additive without using a special material, moreover, even with a small addition amount, conveniently, effectively, the expansion rate of such a general-purpose dental plaster material, in the prior art can be achieved providing high expansion gypsum composition has improved to the extent there was no news, for example, interlocking useful in the generation of replication model to be used to create a "non clasp denture" no problem in (compatible) the provision of the high expansion gypsum composition appropriately control the setting expansion rate to accommodate accurately the shrinkage of the resin used for the purpose, the purpose, which is the main component calcined gypsum, is contained in gypsum powdered gypsum composition material formed on, by co-grinding in a dry, accomplished by the method for manufacturing a high expansion gypsum composition to produce a gypsum composition having an increased cure expansion.特殊な材料を用いることなく安価な添加材で、しかも、少ない添加量でも、簡便に、効果的に、汎用の歯科用石膏材料等の膨張率を、従来技術では達成することができなかった程度まで向上させた高膨張石膏組成物の提供、さらには、例えば、噛み合わせ(適合性)に問題のない「ノンクラスプデンチャー」を作製する場合に使用される複製模型の作製に有用な、使用する樹脂の収縮に精度よく対応できるように硬化膨張率を適宜に制御した高膨張石膏組成物の提供を目的とし、該目的を、主成分である焼石膏に、二水石膏が含有されてなる粉末状石膏組成物材料を、乾式で共粉砕することで、硬化膨張率を高めた石膏組成物を製造する高膨張石膏組成物の製造方法によって達成する。
